The use of carpet on the floor surfaces of both the passenger compartments and the trunks of automobiles is well known. Since around 1956 it has become the practice to mold such carpet to conform to the shape of the floor surface (see U.S. Pat. No. 3,673,034). Frequently it is the practice to adhere a nonwoven felt layer (underpad) to the back of the carpet as the latter is being molded to shape. Such a carpet structure provides resilient, decorative wearing surface with heat insulating and sound deadening qualities.
The carpets used have been of two general types: those having an upper surface (pile) made with yarn tufts anchored in a backing, and those having an upper surface composed of a mass of individual fibers raised above a felted layer of the same fibers. While the pile yarn type of carpet can be made by weaving, knitting or tufting, the tufting process produces most of the pile yarn carpet used in automobiles today and tufted carpet will be used in this disclosure to represent all forms of pile yarn carpet.
The second broad type of carpet is called nonwoven and is made from batts of fiber by needlepunching. No pile yarn is used in making this type of carpet.
In service, rubbing and scuffing tend to pull pile fibers and tufts loose from the back of the carpet, leading to wearing out of the carpet. To minimize this loss of fibers and tufts, it is common practice to apply a back coating to the underside of the carpet. Such a coating is usually of latex or polyethylene.
Latex coatings tend to penetrate readily into the spaces between adjacent fibers in pile yarn or nonwoven felt and also are known to adhere readily to fiber surfaces so that good interfiber bonding is usually obtained with latex coatings. Latex coatings also provide good anchorage of pile yarn tufts (tuftbind) to the textile backing in pile yarn carpets.
Polyethylene coatings generally provide good tuftbind for tufted carpet but only marginal interfiber bonding in both tufted carpet and nonwoven carpet.
Once a carpet structure has been molded to the desired floor shape it is desirable to have the molded product or mat retain a memory for this shape permanently in handling, shipment and storage so that when the mat is installed in the automobile it conforms to the floor contour. The back coating applied to the underside of the carpet is a major factor in achieving this goal. While satisfactory mats have been made using latex coatings, recent manufacturing practice has been designed around polyethylene coated carpet because of the excellent shape retention properties of polyethylene in the temperature range of normal storage and use. Furthermore, the manufacturing process for making satisfactory molded mats with polyethylene back coatings is much more economical and flexible than with latex back coatings since latexed carpet must be dried after molding for satisfactory shape retention while the polyethylene coated carpet needs merely to be heated before molding and then cooled afterward for good shape retention.
The molding of polyethylene carpet is usually accomplished by placing a rectangular blank of carpet face down on a table under a radiant heater which brings the surface temperature of the polyethylene coating approximately to 400.degree. F. The heated blank is then placed face up on a bottom mold and a top, mating mold is brought down so as to mold the carpet blank into the desired shape. When the molded carpet is cool, it retains this shape during storage, shipment and installation.
The polyethylene coating has the additional advantage of becoming tacky when hot so that it acts as the adhesive to bond the underpad to the carpet during the mat molding operation. In the mat molding operation the underpad is placed in the bottom mold as a separate layer before the hot carpet is introduced.
While the underpad, which makes the primary contribution to heat insulation and sound deadening, usually has been made with nonwoven needlepunched felt of inexpensive fibers such as jute, cotton and reused synthetic fibers, various synthetic foam layers have also been employed to a limited extent. These synthetic foam layers have been adhered to the back of the molded mat in the same manner as the nonwoven felt and generally have been of low density. Such use of synthetic foam layers has not been successful because the separate layer of foam does not deform readily in molding.
Since the emergence of flexible polyurethane foams, attempts have been made to produce molded mats with polyurethane foam underpadding directly adhered to the back of the carpet because polyurethanes are known to bond strongly to fiber and other surfaces. In the manufacture of polyurethane foams a solid is formed from a liquid mix by chemical reaction. When the chemical reaction is complete, the product is said to be cured. While the polyurethane foam is still in the liquid state it can be induced to penetrate the spaces between fibers in yarns or felts so as to provide a good interfiber bonding when cured (see U.S. Pat. No. 3,705,834). In addition, once polyurethane foam has been cured in one shape it resists being deformed permanently into another shape. These features early led to attempts to use polyurethane foam to provide fiberbond, tuftbind, sound deadening and shape retention in molded mats.
Three basic approaches have been employed in these attempts:
1. Cast a polyurethane foam layer on the back of the carpet while the carpet is in a horizontal position and, after the foam has cured, mold a section of the carpet-foam composite to the desired shape between mating molds.
2. Cast a polyurethane foam layer on the back of the carpet while the carpet is in a horizontal position and, while the foam is only partiallly cured, mold a section of the carpet-foam composite to the desired shape in mating molds and allow the foam to cure between the mating molds (see U.S. Pat. No. 3,175,936).
3. Deposit a polyurethane foam layer on the nonplanar surface of a bottom mold and, while the foam is only partially cured, place a section of carpet on top of the foam layer and mold the carpet into adhering contact with the foam layer and allow the foam to cure between the mating molds (see U.S. Pat. No. 3,046,177).
None of these methods have been successful. In the first method the carpet-foam composite did not retain the new shape after being removed from the mating molds. Even though thermoplastic formulations of polyurethane foam were used, the foam layer "remembered" the flat shape in which it was cured in preference to the molded shape.
The second method produces a permanently molded product but is not a practical production method both because the carpet-uncured foam composite must be used immediately and because curing in the molds greatly increases the cost of equipment required.
The third method also produces a permanently molded product but is not a practical production method because of greatly increased equipment costs arising from the need to have a foaming head for each pair of mating molds and the curing time increases the number of molds needed for a given amount of production.
It has therefore been the object of the invention to produce a composite carpet structure having not only good fiberbond, tuftbind and sound deadening qualities but also the capability of being deformed to nonplanar shapes permanently by hot molding as well as permitting the ready adherence of an underpad during molding.